The present invention relates to a rolling assembly formed primarily of a tire, a rim and an adapter between the rim and the tire.
A tire commonly used nowadays comprises primarily a tread intended to provide contact with the ground, the tread generally being reinforced by a tread reinforcement, also referred to as a crown reinforcement, which makes it possible to impart to the crown the rigidity in three dimensions which is necessary for rolling of the tire. The crown reinforcement also controls the radial expansion of a carcass reinforcement, which is generally made up of one or more plies of radial reinforcement elements. The carcass reinforcement contains the inflation agent within reasonable limits of deformation of the tire when static and during travel. As is known, the carcass reinforcement is generally anchored within each bead to a reinforcement ring, the beads ensuring the contact with the rim and flange of the mounting rim of the tire.
The transmission of the mechanical forces between the tire and the rim, resulting from the inflation, loading and travel of the tire, and the airtightness of the tire are ensured by the distribution and the magnitude of the contact forces between the bead and the rim seat and rim flange. Good behavior of the tire, both from the point of view of service life and from the point of view of properties imparted to the vehicle fitted therewith, and a good quality/price ratio of the mounting rim have resulted in the adoption of a ratio of rim width to maximum axial width of the tire of close to 0.7. It is clearly known that this ratio is merely a compromise, and that a certain number of properties of the tire, for example its road-holding characteristics, are improved by using a rim which permits a higher ratio. Reciprocally, other properties may be improved, obviously to the detriment of the former, by use of a narrow rim; that is to say, leading to a ratio, as defined above, of close to or less than 0.40.
French Patent 1,267,264, in order to impart to a tire the opposing properties of comfort, road-holding, low rolling resistance and high wear resistance, discloses an outline solution, consisting of imparting to the carcass reinforcement a structure which effectively opposes the transverse flexibility without adversely affecting the radial structural flexibility. Such structure is obtained by superposing on the initial structure of radial reinforcement elements in the carcass reinforcement a secondary structure of inextensible circumferential reinforcement elements. The secondary structure may, furthermore, modify the shape of the sidewalls of the tire, which shape is imparted by the meridian profile of equilibrium of the center axis of the carcass reinforcement. Inextensible, circumferential reinforcement elements of a diameter substantially equal to or less than the diameter of the rim flange, which are arranged radially and axially to the inside of the radial elements of the carcass reinforcement, enable the carcass reinforcement to have a meridian profile which forms a tangent virtually horizontally to the annular anchoring element of the carcass reinforcement.
The foregoing principle is taken up in U.S. Pat. No. 3,486,547, and more particularly with application to a width of the mounting rim which is substantially less than the width of the tread, the ratio of the rim width to the maximum axial width of the tire, in the example given, being 0.41. Although it has advantageous properties, such tire is not without its disadvantages as far as the ability to steer the vehicle fitted therewith is concerned. This results because the reinforcement structure intended to stabilize the secondary structure has a very high rigidity of extension, and a significantly lower compressive strength, in the circumferential direction. The difference in the modulus of the reinforcement structure, depending on whether one is in extension or in compression in the radial direction, means that significant ovalisation of the outer lower part is observed when such a tire is subjected to a vertical load. Upon application of a transverse force to such an axially loaded tire, a non-linear response of the tire occurs depending on whether the force applied has or has not been sufficient to place back under tension that part which was placed under compression during ovalisation.
In order to overcome the foregoing disadvantages of the prior art, the present invention proposes dissociating, within a tire as described above, that part which may be considered as working really like a tire from the part which may be considered as working like a rim. The rolling assembly according to the invention is formed of a tire, a narrow rim, the width of which is at most 50% of the maximum axial width of the tire inflated to its operating pressure, and two connecting elements or adapters which form the join between the mounting rim and the beads of the tire, which adapters are formed of reinforced rubber mixes that are elastically deformable at least in both the radial and axial directions.
As used herein, the terminology xe2x80x9cadapter which is elastically deformable in both the radial and axial directionsxe2x80x9d is to be understood to mean an adapter which permits displacement between the bead of the tire and the mounting rim in the radial direction of at least 5% of the deflection of the loaded tire at recommended load and pressure, and in the axial direction movement of the bead and the rim towards each other of a value at least equal to 15 mm at zero pressure, such deformations being cancelled out if the stresses or forces which cause them are suppressed.
The narrow rim may be of different types: it may be formed, as is known per se, of two rim seats that are extended axially to the outside by two rim flanges directed radially towards the outside and joined axially to the inside by a mounting groove. The presence of a mounting groove may prove not to be necessary, in which case the two seats may be extended axially and radially towards the inside by two radial discs attached by bolts. The two rim seats may also be extended axially towards the inside by two flat parts, which in turn are extended axially and radially by two radial annular discs that are axially spaced apart and permit the fixing thereto of a bead-clamping plate which may complete the rim and may possibly act as a bearing support for the tread in the event of the tire travelling at low or even zero pressure. The plate may be composed circumferentially of a plurality of independent parts.
The mounting rim may also be of the type having a rim with flanges that are directed radially towards the inside, as described and illustrated in French Patent 2,610,872, the beads of the tire in such case becoming lodged on the rim seats via the inside.
In accordance with the invention, a connecting element or adapter between a tire bead and the narrow mounting rim preferably includes primarily a bead, which ensures hooking of the adapter to the rim, and a reinforcement structure, which permits deformation at least in both the radial and axial directions, and creates the connection proper between the bead and a metal reinforcement of the adapter intended to receive the tire bead. The makeup of the bead of the connecting element or adapter is a function of the hooking system of the mounting rim, but preferably comprises a circumferential anchoring ring that may be a simple ring of rubber mix, whether reinforced or not, or a bead wire or a stack of circumferentially oriented reinforcement elements. Around the anchoring ring, by turning-up, or between the reinforcement elements of the ring, by clamping, there is anchored the reinforcement structure of the adapter. The reinforcement structure may be the same components as those used for a known tire carcass reinforcement, that is to say, one or more plies of reinforcement elements that are radial or crossed from one ply to the next, forming a given angle with the circumferential direction of the tire. Such reinforcement elements may be textile and/or metal and/or plastic elements, in the form of monofilaments and/or cables and/or slices.
The second edge of the reinforcement structure of the adapter is joined to an adapter reinforcement. The terminology xe2x80x9cadapter reinforcementxe2x80x9d as used herein is to be understood to mean an assembly formed of at least one rim seat, such seat possibly being extended axially to the outside by a rim flange, with the rim flange possibly being of low height and of conventional shape, in particular curved at its end. The adapter reinforcement may be of metal coated with a rubber mix. The edge of the reinforcement structure of the adapter is anchored to the adapter reinforcement either by superposition radially to the outside, or by winding about the flange, if there is one, the bead of the tire being applied upon mounting on the reinforcement structure of the adapter.